1. Field of the Invention
The present invention relates to a transmitter which can lower output signal distortion, and an associated method.
2. Description of the Prior Art
In wireless communication systems, a transmitter has a power amplifier at the output terminal for amplifying a signal to be transmitted before outputting it. Because the power amplifier has reduced linearity when the input power is strong, nonlinear distortion occurs which affects the data correctness of the outputted amplified signal. Therefore, prior art methods install a pre-distortion circuit before the power amplifier to compensate for this non-linear distortion. FIG. 1 is a diagram illustrating a pre-distortion circuit 110 and a power amplifier 120 and an input versus output curve. As shown in FIG. 1, the linearity between the input signal V1 and the output signal V3 for the whole circuit (including the pre-distortion circuit 110 and the power amplifier 120) is improved, which increases the data correctness of the output signal V3.
In Orthogonal Frequency-Division Multiplexing (OFDM) of third and fourth generation wideband wireless communication, a power amplifier with high power has a memory effect as well as the non-linearity issue, where the response of the power amplifier corresponding to the current input is related to the prior input. In addition, carrier aggregation techniques developed for Long Term Evolution-Advanced (LTE-A) mean that bigger challenges must be overcome when compensating non-linearity of the power amplifier.